The invention relates to a disc brake of hydraulic self-energizing design with a parking brake device.
A disc brake with an electromotive actuator of self-energizing design and with a brake-internal hydraulic arrangement is described in the applicant's application WO 2007/045430 A1.
An immobilizing or parking brake device of a brake disc of this type requires relatively high outlay in terms of components, and assembly and calibration time associated therewith.
It is the object of the present invention to improve a parking brake device of a generic disc brake.
It is thereby possible to realize a parking brake device which permits the construction of a compact disc brake with a smaller number of parts than in the prior art.
According to the invention, the disc brake is provided with a parking brake device with an adjustable screw spindle for adjustment of the at least one brake pad. Here, the screw spindle is, in a particularly space-saving manner, integrated into the at least one brake-application cylinder. The screw spindle can moreover be coupled to the electromotive actuator in order to be driven, wherein a tangential force absorption cylinder can be hydraulically connected to a reservoir circuit and to an expansion vessel.
A disc brake of self-energizing construction comprises the following: a brake-internal hydraulic arrangement with a reservoir circuit and an expansion vessel; a brake-application device having at least one brake-application cylinder for the brake-application movement of at least one brake pad in the direction of a brake disc; at least one force transmission unit which supports the at least one brake pad on the brake-application device at a wedge angle; at least one tangential force absorption cylinder for wedge angle switching, which tangential force absorption cylinder is operatively connected to the at least one force transmission unit; an electromotive actuator which acts on the brake-application device via the hydraulic arrangement; a distributor cylinder for pressure boosting, which distributor cylinder is arranged in series between the electromotive actuator and the brake-application device; and a control unit which is provided for controlling the wedge angle switching between the tangential force absorption cylinder and the electromotive actuator, has a parking brake device having an adjustable screw spindle for adjusting the at least one brake pad, wherein the adjustable screw spindle can be coupled to the electromotive actuator in order to be driven, and wherein the at least one tangential force absorption cylinder can be hydraulically connected to the reservoir circuit and to the expansion vessel.
It is furthermore provided that the at least one force transmission unit is operatively connected to the at least one brake pad by way of a wedge-shaped support device with a supercritical angle form. It is thereby ensured that the parking brake device can remain in the applied state without hydraulic action, and thus requires no energy to maintain the state.
It is thus possible, likewise in a space-saving manner, for an adjustment drive wheel to be formed, together with a shaft drive wheel which is coupled to the screw spindle, as a hydraulic gear motor which can be hydraulically coupled to the electromotive actuator by way of a hydraulic switch. The hydraulic switch can preferably be controlled by the control unit.
A great advantage is that the drive of the parking brake device is realized hydraulically. The gear motor can be of flat construction, and the hydraulic lines can be integrated into the housing.
In a preferred embodiment, the control unit may have a control disc which can be driven hydraulically, by way of a control drive in the form of a hydraulic gear motor, by the electromotive actuator via a switching valve. It is possible in this way, by way of simple control means, for the electromotive actuator to be used as a drive for different tasks. In this case, the electromotive actuator, in addition to its function as a pressure generator for the brake-application device, acts as a drive source for the parking brake device and the control device.
The parking brake device may be provided with an emergency release device, which is preferably coupled to the adjustment drive wheel. In this way, not only is a manual release of the brake possible in the event of an emergency, but a resetting of the brake-application device is also possible for example in the event of a pad change.
For an intelligent follow-up movement in the event of wear of the brake pads (and also of the brake disc), the parking brake device is equipped with at least one sensor. The sensor may for example be formed so as to measure the present fill level in the expansion vessel. For this purpose, the expansion vessel has a suitable fill level sensor, for example a float in conjunction with an electric signal transducer (capacitive, inductive, ohmic resistance). The follow-up movement through a present readjustment travel takes place automatically after every release of the parking brake in that, during the release, the brake pad is raised to a defined distance from the brake disc by way of rotation of the spindles. Subsequently, by the hydraulic actuation of the brake-application cylinders, the contact point of the brake pads with the brake disc is detected and stored in a control unit. The liquid level in the expansion vessel again serves as a travel sensor here. In this way, the brake control unit can always set the brake pad with its required air play. The parking brake device thus also has the function of wear-compensating readjustment. The extent of the pad wear may be measured by measuring the remaining oil quantity in the expansion vessel while the brake is not actuated.
The parking brake device may furthermore have a readjustment piston which can be hydraulically adjusted in the tangential force absorption cylinder during a follow-up movement of the at least one brake pad. Position regulation for a stepped absorption piston of the tangential force absorption cylinder is thus realized in a simple manner, such that the stepped absorption piston, despite occasional pad wear-compensating readjustment, can follow the movement profile of the diverting lever without being hindered by its mechanical stops.
The parking brake device can be released by use of the electromotive actuator. Here, simultaneously, firstly a high hydraulically generated brake-application force is generated by way of the stepped piston, while at the same time the hydraulic gear motor exerts a release torque on the screw spindles for the release of the brake.
It is furthermore advantageous for the mechanical limitation of the horizontal deflection of the brake pad as a result of an ever increasing tightening action to lead, owing to a supercritical wedge angle, to a high braking force, which however simultaneously prevents overloading.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.